The present invention relates to improvements in apparatus for examining discrete portions of information, especially for examining discrete frames on webs or strips consisting of one or more exposed and developed photographic films. More particularly, the invention relates to improvements in apparatus for producing correction signals for reproduction of film frames or the like in copying machines. Still more particularly, the invention relates to improvements in manually actuatable apparatus which can be used to produce signals based on subjective (visual) inspection of discrete portions of information, especially frames of black-and-white or color photographic films.
It is known to equip a copying machine for the frames of photographic films with a prereader which automatically examines successive frames of an elongated web (the web may consist of a single film but it preferably includes a large number of films which are spliced together end-to-end). The prereader can be installed ahead of the copying machine and is then associated with a suitable data carrier (e.g., magnetic tape, punched tape or magnetic disk) which stores the correction signals in encoded form so that the stored information may be decoded by an automatic reader of the copying machine when the corresponding frames of the web reach the copying station. Alternatively, the prereader can be integrated into the copying machine and transmits appropriate correction signals directly to the exposure controls.
A drawback of automatic prereaders which are integrated into or are independent of copying machines is that the correction signals which are produced therein are not always satisfactory for proper reproduction of film frames. As a rule, one out of 10 film frames which are reproduced in accordance with correction signals furnished by an automatic prereader is unsatisfactory. The reasons for failure of the prereader to furnish appropriate correction signals for each and every frame of one or more photographic films are manifold. For example, the prereader cannot discriminate between color film frames wherein a primary color dominates over the other primary colors and color film frames with an undesirable color shade. Also, the prereader cannot discriminate between frames wherein the density of a particular frame portion or field should deviate considerably from the density of other portions and film frames which can be properly reproduced only if the density of certain portions is reduced or increased. For example, let it be assumed that the density of the most important portion of a film frame deviates considerably from the density of the other part or parts of the same frame, e.g., that the density of the central portion of the photographed Scene or subject is substantially different from the density of the foreground and/or background. If such a frame is reproduced on the basis of information which is supplied by an automatic prereader, the latter will determine the average density of the entire film frame and will produce a corresponding correction signal.
It was already proposed to divide each film frame into several imaginary fields or areas and to determine the density of each field independently of the others. The commonly owned U.S. Pat. No. 3,523,728 to Wick et al. discloses an apparatus which determines the density of a relatively small first portion of each film frame and the tonal distribution of a larger second portion of the same frame. The density of reproduction is determined on the basis of reading of the first portion and the color balance of the print is determined on the basis of reading of the second portion.
U.S. Pat. No. 3,790,275 to Huboi et al. discloses an apparatus which includes three radiation sensitive devices one of which receives radiation from the upper portion of the frame, another of which receives radiation from the lower portion of the frame, and the third of which receives radiation from the central portion of the frame. Thus, the patented apparatus measures the density of the central portion (which is normally the most important part of the frame) independently of the first (upper) and second (lower) portions. Such mode of examining film frames will result in the making of satisfactory reproductions if the camera is always held in the same position whenever the user makes an exposure. This normally holds true when the film in the camera contains square film frames, i.e., the user of the camera is less likely to turn the camera through 90.degree. or upside down if the width of each frame is the same as its height. However, when the film contains rectangular frames, the user is highly likely to change the position of the camera during the making of exposures, usually through 90.degree.. However, it happens again and again that an exposure is made with the square or rectangular frame held upside down, i.e., at 180.degree. to the normal or expected position. The aforediscussed apparatus are then incapable of furnishing satisfactory correction signals because they confuse the foreground with the background (in the case of inverted shots) or a portion of the foreground with a portion of the background (in the case of exposures made with the camera held at an angle of 90.degree. with respect to the normal position). A camera which accepts films with rectangular frames is expected to be held in such position that the longer sides of each frame are parallel with the direction of film transport. Thus, the foreground is located in the lower part, the background in the upper part and the (normally most important) central portion of the photographed scene is located at a level between the upper and lower parts. If the camera is turned through 90.degree. so that the user can make an upright exposure, the foreground is located at one end and the background is located at the other end of the respective frame, as considered in the direction of film transport. If such film frame is introduced into an automatic prereader, the prereader will interpret one-half of the foreground as the background and vice versa.